The present invention relates generally to motor vehicle propeller shafts, and more particularly to an apparatus for absorbing energy within a propeller shaft of a motor vehicle.
Two-piece propeller shafts are commonly used in motor vehicle propulsion. The two-piece propeller shaft is used when larger distances exist between a front drive unit and the rear axle of the vehicle. The two-piece propeller shaft transmits torque from the front drive unit to a rear axle. The two-piece propeller shafts are typically supported by a center-bearing and corresponding support bracket. The center-bearing and support bracket support the center of the propeller shaft while still allowing the drive shaft to rotate and transfer mechanical energy from the front drive unit to the rear axle.
Besides transferring mechanical energy, it is desirable for propeller shafts to have adequate crashworthiness, be lightweight, easy and inexpensive to manufacture, and have adequate noise vibration and harshness (NVH) characteristics.
With regard to crashworthiness, it is desirable for the propeller shaft to be shortened axially to prevent it from buckling, penetrating the passenger compartment, or damaging other vehicle components in close proximity to the propeller shaft. As well, it is desirable for the shaft to absorb a considerable amount of the deformation energy.
Current designs produce a significant amount of noise and vibration that is transferred from the rotating propeller shaft to the motor vehicle. The noise and vibration is caused by a cantilever effect created by a bulk of the propeller shaft mass located a designed distance away from a center-bearing support bracket. The distance creates a cantilever arm, which increases the force of the rotating propeller shaft on the center-bearing support bracket, thereby increasing noise and vibration transferred to the motor vehicle. Imbalance of the propeller shaft can also be attributed to causing noise and vibration. However, balancing conventional propeller shafts is difficult and time consuming. To reduce noise and vibration, isolators are installed between the center-bearing support bracket and the center-bearing. The isolators in some cases are required to be balanced with the propeller shaft, which increases time and difficulty of installation.
Improved crashworthiness, reduced cost to produce and assemble, and reduced NVH are continuous ongoing concerns for vehicle powertrain engineers. Thus, there exists a need for a two-piece propeller shaft that is able to accommodate the above listed propeller shaft requirements, reduce noise and vibration transfer, and increase ease of assembly. If the above improvements can be achieved, the safety of motor vehicles may be increased, the cost of manufacturing can be reduced, and the NVH of the propeller shaft can be reduced.
Accordingly, an object of the present invention is to provide an improved propeller shaft assembly. An advantage of the present invention is that it provides improved crashworthiness, reduced NVH, and is easier to manufacture than existing two-piece propeller shaft assemblies.
The foregoing and other objects and advantages are provided by an apparatus for absorbing energy within a propeller shaft of a motor vehicle. A propeller shaft assembly including a constant velocity universal joint in a propeller shaft of a motor vehicle connecting a drive unit to a rear axle gearbox is provided. The universal joint includes at least two articulatably connected shaft portions, a hollow shaft, and a connecting shaft. The hollow shaft is connected to an outer joint part that has outer ball tracks. The hollow shaft has an aft open area and an exterior wall. The connecting shaft is connected to an inner joint part that has inner ball tracks. A plurality of torque transmitting balls are held by a cage and each are guided in one pair of corresponding outer and inner ball tracks. The ball cage holds the balls in a plane when the inner joint part is axially displaced or articulated. A standard plunge is included which is usable within a normal operating range in a damage-free way. The plunge has a fore plunge portion defined by a plane at a second stop, and an aft plunge portion defined by a plane at a first stop. The aft plunge portion and the aft open area having inner diameters that are greater then or equal to an inner diameter of the outer joint part. When the outer joint part is displaced relative to the inner joint part the movement of the balls is limited in an aft direction relative to the hollow shaft by the first stop to remain within the normal operating range. The first stop is forcibly displaceable, however, such that the connecting shaft may release the first stop and intrude significantly within the aft open area which is beyond the normal operating range.
One of several advantages of the present invention is that it may forcibly collapse within itself at a predetermined load.
Another advantage of the present invention is that it minimizes the number of components used as compared to conventional shaft assemblies, thereby reducing mass and imbalance of the vehicle propeller shaft. Reduced mass and imbalance improves quality, decreases noise and vibration, and reduces costs in production and manufacturing of the propeller shaft.
Another advantage of the present invention is that the majority of the mass of the propeller shaft assembly is directly supported by the center-bearing, providing improved balance and decreased noise and vibration.
The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawings.